Crystal microphone with automatic silencer



Oct. 1.4, 1969 c. Noss 3,472,972

CRYSTAL MICROPHONE WITH AUTOMATIC SILENCER Filed Dec. 13, 1965 PRIOR ART United States Patent Othce 3,472,972 CRYSTAL MICROPHONE WITH AUTOMATIC SILENCER Cornelius Noss, Munich, Germany, assignor to Siemens Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed Dec. 13, 1965, Ser. No. 513,266 Claims priority, applicgtigorfrmany, Dec. 12, 1964,

Inf. C1. H641 15/02 U.S. Cl. 179-110 10 Claims ABSTRACT F THE DISCLOSURE A coupling abuts the crystal of a microphone and moves with the sound wave responsive diaphragm to apply pressure to the crystal when sound waves strike the diaphragm and apply thereto a pressure less than a determined magnitude. The coupling disengages from the diaphragm to permit free movement of the diaphragm when sound waves strike the diaphragm and apply thereto pressure eonal to or greater than the determined magnitude.

crystal microphone with an automatic silencer which operates with etiiciency, eiectiveness and reliability.

Another object of the present invention is to provide a crystal microphone with an automatic silencer of very simple structure.

In accordance with the present invention, the microphone comprises a mechanical-electrical transducer crystal fixedly mounted in the microphone. A sound wave responsive diaphragm is mounted in the microphone for displacement toward the crystal when struck by sound waves. A coupling abuts the crystal and moves with the sound wave responsive diaphragm to apply pressure to the crystal when sound waves strike the diaphragm and apply thereto a pressure less than a determined magnitude and disengages from the diaphragm to permit free movement of the diaphragm when sound waves strike the diaphragm and apply thereto a pressure equal to and greater than the determined magnitude.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein:

FIG. 1 is a view, partly in section, of part of a crystal microphone of the prior art;

FIG. 2 is a view, partly in section, of an embodiment of the crystal microphone of the present invention;

FIG. 3 is a View, partly in section, of another embodiment of part of the crystal microphone of the present invention; and

FIG. 4 is a View, partly in section, of still another embodiment of part of the crystal microphone of the present invention.

In the figures the same components are identified by the same reference numerals.

In the prior art crystal microphone of FIG. 1, a sound wave responsive member or diaphragm 1 may ebe of substantially disc-like configuration. The diaphragm 1 is mounted in the microphone at its peripheral area, edge or rim so that it is displaced toward the crystal 3 when 3,472,972 Patented Oct. 14, 1969 struck by sound waves 12. The crystal 3l is a piezoelectric or piezoresistive crystal well known and in a well-known application in a microphone and is tixedly mounted in the microphone. The crystal 3 may comprise the semiconductor body of a transistor. In such case, the diaphragm 1 is coupled to the transistor in a manner whereby the pressure of sound waves on said diaphragm produces a mechanical stress in said transistor, which produces an electrical current or voltage signal modulated in accordance with variations of said pressure of sound waves.

A coupling pin 2 is aixed to the diaphragm 1 at its axis, the pin 2, crystal 3 and diaphragm 1 being coaxially positioned in the microphone. The axis of the diaphragm 1 is, of course, the point of maximum displacement or oscillation of Said diaphragm when said diaphram is struck by sound waves. The coupling pin 2 is so dimensioned, in a well-known manner, that low intensity or low amplitude sounds, or high intensity or high amplitude sounds, which produce small pressures and large pressures on the diaphragm 1, produce a mechanical stress in the crystal 3 which varies as the intensity or amplitude of the sound. The crysal 3 is electrically coupled by any suitable means such as, for example, capacitive or galvanic means, with an electrical circuit 13, which provides an electrical signal modulated in accordance with the intensity or amplitude oi the sound waves striking the diaphragm 1.

The mechanical stress produced on the crystal 3 by sound having an excessively high intensity or amplitude overstresses said crystal and said crystal fails to produce a corresponding electrical sginal and :may be damaged. In accordance with the present invention, the microphone is provided ywith an automatic silencer which abuts the crystal and moves with the diaphragm to apply pressure to the crystal when sound waves striking the diaphragm apply thereto a pressure less than a determined critical magnitude and disengages from the diaphragm to permit free movement of the diaphragm when sound waves striking the diaphragm apply thereto a pressure equal to and greater than the determined critical magnitude.

In FIG. 2, the diaphragm 1 is mounted as in FIG. 1 except that it has an aperture 6 formed therethrough and is covered by a cover portion 5 which is tixedly mounted on the microphone spaced from said diaphragm. The cover portion 5 permits sound waves to pass therethrough to the diaphragm 1. Thus, the cover portion S may, for example, have perforations formed therethrough, as shown. The cover portion 5 has a cup-like recess 14 formed therein at its axis.

The mechanical-electrical transducer crystal 3 is coaxially supported in a crystal support 9 in a resilient support disc-like member 7, each of which is xedly positioned in the microphone coaxially with the diaphragm 1. An axially extending adjusting screw 8` is threadedly coupled to the crystal support 9 and is movably supported by the housing 11 of the microphone. Thus, by rotation of the adjusting screw 8 and tightening of the nut 10, an attendant may adjust the position of the crystal 3 and maintain said crystal in its adjusted position; rotation of said adjusting screw causing said screw to move in an axial direction and moving said crystal in the same direction due to the resiliency of the resilient support member 7. The `adjusting screw 8 and the resilient support member 7 are preferably electrical conductors and are insulated; the adjusting screw being supported by electrical insulation washers.

The mechanical coupling 2 between the diaphgram 1 and the crystal 3 comprises a cup 2b positioned through the 'aperture 6 of said diaphragm. The cup 2b has an inside or upper surface, an outside or under surface and a peripheral flange or lip 2c which supports said cup in position on the diaphragm 1. The mechanical coupling sa 2 further comprises a pin 2a extending axially from the outside surface of the cup 2b, through the aperture 6, and abutting the crystal 3. A spring 4 is axially positioned in the microphone between the cup 2b of the coupling 2 and the recess 14 of the cover portion 5. One end of the spring 4 abuts the under surface of the recess 14 and the other end of said spring abuts the inside surface of the cup 2b.

The spring 4 of the mechanical coupling 2 urges the cup 2b against diaphragm 1 and the pin 2a abuts the crystal 3 with varying pressure in accordance with the varying pressure of sound waves striking said diaphragm. The force of the spring 4 is determined to prevent influence upon the operating efficiency of the microphone and to prevent crystal damage. Since the peripheral flange or lip 14 of the cup 2b is of greater diameter than the laperture 6 of the diaphragm 1, said lip rests on said diaphragm and insures, with the spring 4, displacement of said cup and the pin 2a with said diaphragm under the iniiuence of sound waves striking said diaphragm. The cup 2b and pin 2a are displaced with the diaphragm 1 for all sound intensities, amplitudes, volumes or pressures less than a determined critical magnitude. The force of the spring 4 determines the critical magtude.

When the sound intensity, amplitude, volume or pressure, indicated by sound waves striking the diaphragm 1, is equal to or exceeds the determined critical magnitude, the coupling 2 disengages from the diaphragm to permit free movement of the diaphragm. The excessive sound wave pressure displaces the diaphragm 1 toward the crystal 3, but the spring 4 maintains the cup 2b and the pin 2a at the critical position so that said cup and said pin remain stationary and do not move with said diaphragm. The excessive sound wave pressure is thus not transmitted to the crystal 3, but is dissipated in free displacement of the diaphragm. The force of the spring 4 is less than one which would damage the crystal and is slightly greater than the sum of the pressure of the pin 2a on the crystal 3 and the maximum pressure of sound waves on the diaphragm 1 less than the determined critical magnitude.

In the embodiment of FIG. 3, the diaphragm 1 has the aperture 6 formed therethrough at its axis. The coupling 2 of the embodiment of FIG. 3 may be said to provide movement of the diaphragm 1 which is partially free when the sound intensity, amplitude, volume or pressure exceeds the determined critical magnitude, as distinguished from the full freedom of movement provided by the embodiment of FIG. 2. The coupling 2 comprises a plate 16 affixed to the diaphragm 1 and covering the aperture 6 therethrough at a distance from said diaphragm. A pin support 17 rests on and is supported by the diaphragm 1 over the aperture 6. The pin 2a extends axially from the under surface of the pin support 17, through the aperture 6, `and abuts the crystal 3.

A sprin-g 18 is axially positioned in the microphone between the plate 16 of the diaphragm 1 and the upper surface of the pin support 17. One end of the spring 1S abuts the under surface of the plate 16 and the other end of said spring abuts the upper surface of the pin support 17. The pin support 17 may be of substantially disc-like configuration. The spring 18 biases the pin support 17 against the diaphragm 1 and the pin 2a abuts the crystal 3 with varying pressure in accordance with the varying pressure of sound waves striking said diaphragm. Since the pin support 17 has a greater diameter than the aperture 6 of the diaphragm 1, said pin support rests on said diaphragm and insures, with the spring 18, displacement of said pin suport and the pin 2a with said diaphragm under the influence of sound waves striking said diaphragm.

The spring 18 of the embodiment of FIG. 3 functions similarly to the spring 4 of the embodiment of FIG. 2,

and the embodiment of FIG. 3 functions similarly to the embodiment of IFIG. 2, except that the spring 18 moves in its entirety with the diaphragm 1 in the embodiment of FIG. 3 so that partial freedom of movement of the diaphragm is provided by the coupling 2 of FIG. 3 when the pressure of sound 'waves striking the diaphragm equals or exceeds the determined critical magnitude.

In the embodiment of FIG. 4, the diaphragm 1 has the aperture 6 formed therethrough at its axis. The coupling 2 is fully disengaged from the diaphragm 1 when the sound intensity, amplitude, volume or pressure exceeds the determined critical magnitude, as provided y by the embodiment of FIG. 2. The coupling 2 comprises a pin support 19 which rests on and is supported by the diaphragm 1 over the aperture 6. The pin 2a extends axially from the under surface of the pin support 19, through the aperture 6, and abuts the crystal 3.

The pin support 19 is magnetically attracted in the direction of the crystal 3, The magnetic attraction may be provided by any suitable means such as, for example, a magnetic pin support 19 and a magnetic member between thediaphragm and the crystal 3. Thus, for example, the pin support 19 may comprise a ferromagnetic material. A guide 20, of ring shape, surrounds the pin 2a and is iixedly supported between and spaced from the diaphragm 1 and the crystal 3. The guide 20 comprises a magnetic material which may be similar to the magnetic material of the pin support 19. Since the pin support 19 is of substantially disc-like configuration and has a greater diameter than the aperture 6 of the diaphragm 1, said pin support rests on the diaphragm and insures, with the magnetic force, displacement of said pin support and the pin 2a with said diaphragm under the influence of sound waves striking said diaphragm.

The magnetic force urges the pin support 19 against the diaphragm 1 and the pin 2a abuts the crystal 3 with varying pressures in accordance with the varying pressure of sound waves striking said diaphragm. The magnetic force is determined to function in the same manner as the force of the spring 4 of the embodiment of FIG. 2. The magnetic force is thus determined to prevent influence upon the operating eiiiciency of the microphone and to prevent crystal damage. The pin support 19 and pin 2a are displaced with the diaphragm 1 for all sound intensities, amplitudes, volumes or pressures less than a determined critical magnitude, The magnetic force determines the critical magnitude.

When the sound intensity, amplitude, volume or pressure, indicated by sound waves striking the diaphragm 1, is equal to or exceeds the determined critical magnitude, the coupling 2 is fully disengaged from the diaphragm. The excessive sound wave pressure displaces the diaphragm 1 toward the crystal 3, but the magnetic force maintains the pin support 19 and the pin 2a at the critical position so that said ypin support and said pin remain stationary and do not move with said diaphragm. The excessive sound wave pressure is thus not transmitted to the crystal 3, but is dissipated in free displacement of the diaphragm. The magnetic force is less than one which would damage the crystal and is slightly greater than the sum of the pressure of the pin 2a on the crystal 3 and the maximum pressure of sound waves on the diaphragm 1 less than the determined critical magnitude.

While the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim: 1. A microphone, comprising a mechanical-electrical transducer mounted in said microphone;

sound wave responsive means mounted in said microphone for displacement toward said crystal when struck by sound waves; and

crystal iixedly coupling means abutting said crystal and moving with said sound wave responsive means to apply pressure to said crystal when sound waves strike said sound wave responsive means and apply thereto a pressure less than a determined magnitude and disengaging from said sound wave responsive means to permit free movement of said sound Wave responsive means when sound waves strike said sound Wave responsive means and apply thereto a pressure equal to and greater than said determined magnitude.

2. A microphone as claimed in claim 1, wherein said sound wave responsive means comprises a diaphragm.

3. A microphone as claimed in claim 1, wherein said microphone further comprises a cover portion xedly mounted on said microphone spaced from and covering said sound wave responsive means and permitting sound waves to pass therethrough to said sound wave responsive means, and wherein said coupling means includes spring means abutting said cover portion and biasing said coupling means toward said crystal.

4. A microphone as claimed in claim 3, wherein said sound wave responsive means includes an aperture formed therethrough and said coupling means comprises cup means positioned through said aperture and having an inside surface, an outside surface, a peripheral ange supporting said cup means in position on said sound wave responsive means, said spring means abutting said cover portion and the inside surface of said cup means, and pin means extending from the outside surface of said cup means and abutting said crystal.

5. A microphone as claimed in claim 4, wherein said microphone further comprises crystal mounting means including resilient support means xedly positioned in said microphone coaxially with said sound wave responsive means, said crystal being coaxially supported in said support means, and axially extending adjusting means movably supported in said microphone and coupled to said spring means abutting said plate means and said pin support means and biasing said pin means toward said crystal.

6. A microphone as claimed in claim 1, wherein said sound wave responsive means includes an aperture formed therethrough and said coupling means comprises plate means aixed to said sound wave responsive means and covering the aperture therethrough at a distance from said sound Wave responsive means, pin support means supF ported by said sound wave responsive means over said aperture, pin means extending from said pin support means through said aperture and abutting said crystal, and spring means abutting said plate means and said pin support means and biasing said pin means toward said crystal 7. A microphone as claimed in claim 6, wherein said sound wave responsive means comprises a diaphragm.

8. A microphone as claimed in claim 1, wherein said sound wave responsive means includes an aperture formed therethrough and said coupling means comprises pin support means supported by said sound wave responsive means over said aperture, pin means extending from said pin support means through said aperture and abutting said crystal and magnetic means attracting said pin support means in the direction of said crystal.

9. A microphone as claimed in claim 8, wherein Said coupling means further comprises gui-de means xedly supported between and spaced from said sound wave Iesponsive means and said crystal, said guide means comprising ring means surrounding the pin means of said coupling means.

10. A microphone as claimed in claim 8, wherein said sound wave responsive means comprises a diaphragm and said magnetic means comprises said guide means and said pin support means, said pin support and said ring means being magnetic.

References Cited UNITED STATES PATENTS 3,383,475 5/1968 Wiggins -179--110 KATHLEEN H. CLAFFY, Primary Examiner J AN S. BLACK, Assistant Examiner 

